So over the past couple weeks I have noticed that in the morning on my way into work, I am not getting ANY heat till ~10 minutes into my commute of ~30 minutes. Now, my car has never been 'quick' to giving out hot air, even with it set to 84 deg on both sides, but this delay has me wondering where I need to dig. My 2017 has ~67K on the clock and hasn't had a coolant service for reference. Just seeing if anyone has anything to toss out before I start to dig into this a bit further??

I was initially thinking that I may have a clogged heater core, due to the original coolant load, but when I do eventually get heat it is flat out HOT, so the core is flowing/conducting just fine. My dash temp gauge is showing spot on 'normal', but I need to check actual output temp via Bimmer Link yet. When I do have heat, I can also adjust the temp and get plenty of response there, so the blend doors appear to be working just fine. I can also hear them actuate as I sweep the temp control from 60-84 deg settings, yet again telling me they are still operable.

Is there a coolant flow control valve in the system for the heater core in these cars? I am wondering if it is failing/sticking, where it cuts coolant flow to the heater core and take a while to get warm coolant from flowing to the core? Or could it be a temp sensor that is getting slow to react that may control a flow valve? As I noted, just starting to dig into this and looking for some input/feedback. TIA.

 

Long story short: My slow/no heat issue was related to a low coolant level, relatively simple fix of adding more coolant till back up into the normal range between MIN & MAX level indicators.

Long story:

A few weeks ago I noticed on my commute to/from work (~20 miles each way) that it was taking several miles to get heat blowing from the vents. This was a bit of a concern heading into the winter season.

My commute to work starts with 5 miles of side streets, 14 miles of highway driving and finishes with 1 mile of side streets. My heat was luke warm at best when I hit the highway. About 5 highway miles later, I would get decent heat for the remaining 9 miles, but the heat would fall right back off as soon as I got off the expressway and would be ‘cool’ by the time I pulled into the parking lot at work. This same basic temperature pattern repeated on my way home as well, so at least it seemed consistent to engine/vehicle operation vs random…something to work with.

Reading through the various forums for both Mini’s and BMW’s, one topic seemed to pop up was a failed thermostat for similar symptoms. Although most failures seemed to be stuck closed and would overheat the engine…I was having a symptom of a stuck open thermostat, so the search continued.

I am pretty handy at tackling most mechanical jobs on cars, so I looked into the overall design/components of the F54’s system. Holy cow, there is quite the myriad of passages/hoses/connections and components, much more that I have encountered on my previous vehicles. I now have an idea why folks gripe about BMW coolant systems and potential leaks. Anywho, it looks like we have a single thermostat and (2) electric coolant pumps, (1) main pump and (1) aux pump to cool the turbo.

I wasn’t sure I could troubleshoot this, but wasn’t ready to make a call to the dealer just yet. I am well out of warranty and don’t have an extended warranty, so this could hit my wallet pretty hard. I knew I needed to do some more data digging to see what I could find.

Searching further on the interwebs, I found quite a few Mini folks talking about how sensitive our cars are to coolant levels and as soon as you fall below the “MIN” level, you will typically lose cabin heat…interesting. I hadn’t thought of looking at my coolant level yet, since I haven’t had any evidence of leaking coolant under the car nor a leaking head gasket.

Before even looking at that coolant level, I decided to use my BimmerLink app to monitor the actual coolant temp vs the ‘combined’ temperature display on the dash and also watch a digital temp probe in my dash vent for air temps. On my morning commute, the BimmerLink coolant temp came up to 90°C within the first 3 miles of my commute. Its target temperature is 108°C for reference and the outside air temp was 28°F that morning. With the climate controls set to 84°F, fan speed to ‘4’ and vent only position, my dash vent air temp only reached 70°F as I was getting onto the highway at the 5 mile mark of my commute, which is actually pretty cool for air temps. About 1 mile into the expressway portion and my coolant temp settled in at 108°C and held steady for the rest of the 13 mile expressway portion. I cruise at 80mph, which nets ~2200rpm engine speed. My air vent temp moved up quickly and settled in at 145°F by mile 7 of 14 and held there till I exited the expressway. Sitting ~1 minute at the light on the off-ramp, vent temps dropped to 123°F and by the time I pulled into my parking spot at work it was down to 81°F. I sat and idled for 5 minutes and it was down to 76°F. My engine coolant temp was a rock steady 108°C…interesting.

I did the same observation on my way home that day and saw a very similar temperature pattern as well. Just before I got home, I did shift into manual mode on the tranny and ran a steady 3500rpm and the heat came back up to 145°F almost instantly, which virtually cemented the idea of low coolant in my mind.

I let the car cool down a couple hours, opened up the expansion tank cap and noticed there was no coolant in the expansion tank…ZERO…uh oh! I know darn well I don’t have any coolant leaks, as I change my own oil and would have noticed any kind of leaking fluid under there and recently changed my spark plugs and they didn’t show any kind of ‘steam cleaning’ a leaking head gasket would indicate either. I guess the ~6 years and 69K miles has simply evaporated some quantity of coolant and left me short…which would certainly explain the heat performance I had just experienced. Luckily it doesn’t appear to be too low, which would have overheated my engine.

I went out and purchased a bottle of Pentosin Pentofrost NF coolant and some distilled water to dilute to the recommended 50:50 ratio, since the Pentofrost is ‘concentrated’ or non-diluted. I put in an initial 50:50 fill of 32oz to fill most of the expansion tank, but was still well below the MIN marker (wow!). I did a quick drive around to heat cycle the engine/coolant and parked it for the night to allow the system to pull in coolant to displace any air in the system. The next morning it took another 16oz to bring the coolant level between the MIN and MAX levels. I ran some errands that day and let it cool overnight again. The next morning it took another 8oz to bring it back up between the markers again. If you are keeping count, that is a total of 56oz of coolant!! The total system capacity is listed at 5.8L or 196oz for the record. That means I was down just over 28%...no wonder I was having heat issues and was likely close to having engine cooling issues too!

Update 1. On my further commutes, my BimmerLink engine coolant temps are still remaining the same, but now I am seeing 110°F vs 70°F vent temps by the time I get on the expressway, a rock steady 145°F all the way into work and only see it drop off no lower than 138°F after idling in the parking lot for 5+ minutes. I now get heat much, much sooner and RPM no longer creates a vent temp swing, so I will call this case basically shut.

Update 2. I waited 1 week and it took another 4oz of coolant, waited 1 more week and another 4oz of coolant. That brings me to a total of 64oz or 32.6% total system capacity. From here, it will be part of my oil change process to check the coolant level as well!

In any case, I suggest you check your coolant level in your MINI, before you start having issues. My wife and I have owned each of our last (5) new vehicles for 8-11 years and have NEVER had to top them up, so hence the reason I was caught a bit off-guard on this subject. As they say, learn something new every day ;-)

 

Now, where did that coolant go??
Leaks?

Remove your oil filler cap, and look into the hole, make sure you dont see
chocolate milk shake looking fluid in there.

 

That is a great question and I don't have a definitive answer.

I change my own oil and have never found any evidence of coolant in the oil, previously or currently. During oil changes, I pull my underbelly cover and have not seen any evidence of a coolant leak anywhere on the cover or under the engine or chassis. Considering we have a sealed coolant system, I have a hard time believing it has simply 'evaporated', but I honestly don't have any other explanation.

I am about 1 week away from 6 years of ownership from new with a click over 69K on the clock. Is this coolant loss within typical specs for this engine? I wish I knew, but will see if I can dig up some real-world info somewhere along the line. Right now all my other car savvy friends are simply scratching their heads.

The only other example I know of with a 'regular' coolant loss is a friend with a 2015 F-150 w/5.0L Coyote engine. He has owned it since 2018 and had to occasionally top it off with coolant as well. His truck is world's different than my F54, other than it uses a similarly 'sealed' coolant system with a pressurized expansion tank. He too changes his own oil and does his own maintenance and has never found any evidence of an external leak either, but has seen a somewhat regular loss of coolant.

 

Have owned a number of cars over the years and coolant loss of any amount was always due to a leak. Sometimes the leak was not obvious.

A pretty insidious leak arose from a bad cap on the coolant tank reservoir. The cap would vent pressure (and release water vapor -- hence no odor of antifreeze) if I shut off the engine up to temperature. The heat load of the engine would raise coolant temperature and pressure.

Ended up confirming it was the cap by topping up the coolant tank with distilled water. I wanted the level at max but not above. The less air space in the cooling system the better for a hot pressure test. Made sure the cap was on securely. Drove car around town until I could hear the radiator fans come on (at 212F). Back home on my driveway raised RPMs to 1K and kept them there until the radiator fans came on. Then I shut off the engine. I had prepared a "tent" of foil to place over the cap. I didn't suspect the cap but thought the leak might be from the tank under the cap or from the hoses/connections.

After a few minutes the tent had water condensed on its underside. I checked for leaks but found no signs of any. Replaced the cap. No more low coolant levels. And I had some "help" in that there had been reports of a problem developing from the version of the cap. Version -0. -1 never saw the light of day. But reports were the -2 cap worked and didn't leak. So I replaced the original -0 cap with a -2 and as I mentioned above, no more low coolant.

Another time the coolant tank proved to be the source of a leak. Long story short the tank developed a crack along its bottom along the mold seam. Under the right conditions -- very similar to the one that forced water vapor from the cap -- the tank would expand and the crack would open up and let coolant seep out. Never a puddle on the ground. The tank only opened up very slightly and just a bit of coolant leaked out. Because it was hot the water evaporated almost instantly leaving behind just the nasty old sickly greenish deposits. But when I subjected the cooling system to a hot pressure test after just a few moments the tank opened up and gushed hot coolant like an inverted geyser.

Of course the leak can be at a water pump, the seals. And I've had a few radiators develop leaks. One through a pinhole which was hard to spot. But with another car the leaks came from around where the bottom "tank" was crimped to the radiator cooling core. Age and expansion and contraction over time compromise the seal between this tank and the rest of the radiator.

Bottom line is you need to search for and find and fix the leak.

 

Deleted. Duplicate.

 

You might want to also check for any BMW issued TSBs on coolant leaks and if there are any, might be the starting point to investigate.....

 

The owner of a local independent MINI shop near me that has been around for a bit (and the owner himself was in BMW service dept for 10 years prior to that) had this to say to me about finding each time I do an oil change that my coolant is lower than I think it should be: "sees it all the time." Whether a leak or a "leak" his take is that it is characteristic of the MINIs, or at least the one I've got (F56S).

When I did my first maintenance on my F56S (bought used in mid-2021) the coolant level was in the "oh crap where did the coolant go my other car doesn't do that" zone. 5000 miles later it was lower than should be but not like the first time. 5000 miles later than that it was at minimum. Cap issue? I dunno. But nothing on my F56S is in visually discernible disrepair, so I remain mindful that "it's a thing" and look around for other signs of coolant weird at least every time I change the oil (5K mile interval).

Since the F56 and F54 are not even remotely identical, this may not directly apply -- but in the event it might help, hope it helps. I appreciate @RockC 's post up there -- I may just replace my reservoir cap on general principle.

 

Service intervals for my cars has been every 5K miles and this for years. While the tech may have topped up the coolant level when the car was in for service the only time the coolant got low enough to need topping up between services is when the reservoir cap was venting water vapor as the hot engine heated up the coolant and increased its temperature and pressure to the point water vapor was forced out the cap.

So I take a low coolant level between services as a red flag indicating a leak.

Now some techs told me some coolant leakage is "normal". For instance a bit of coolant can leave via the water pump seal. This happens -- like with the reservoir cap -- when the engine is shut off hot. Hot as in the radiator fan is running because the coolant is hot enough to trigger the fan to run. If one drives with the A/C on the fan runs all the time and this keeps the engine cooler. Where I lived in CA the weather was mild and it was low humidity so I could drive with the A/C off quite often. So the radiator fan would come on every so often as the coolant temperature climbed to the fan on threshold (212F) then the coolant temperature would drop as the fan ran. If I just happened to shut off the engine before the fan had run long enough to begin to bring the temperature down then the heat load of the engine would raise coolant temperature and pressure. This can force a bit of coolant out past the water pump seal. The techs said evidence this is happening is a white residue on the water pump. The residue is what is left of the tiny bit of anti-freeze that is carried out with the water. The hot water evaporates.

But the techs stressed there should never be any signs of wetness. Green (or orange or whatever color) coolant residue should not be present.

But as I said above never between 5K mile services has any cooling system needed coolant unless there was a leak. Cap. Bad coolant tank. Bad water pump. Or leaking radiator.

Yes I admit I have really very limited experience with MINI. Just the approx. 25K miles and 29 months I owned my JCW. While my JCW never required coolant between services -- and I don't know if it required any at service I never saw it low when I checked the level -- that doesn't mean all MINIs are equally stingy with coolant. So sure as the shop owner offered it might be normal. If the amount you need to add to bring the level up increases that's a sign the loss is no longer normal.

And an inadequately filled cooling system or one that can't maintain pressure is a real concern, and needs to be addressed promptly.

 

Hey ​​​​@RockC - got an update for you.

I was under the hood doing "stuff" with the car cold and happened to accidentally tap the coolant reservoir. Started hearing a very quiet sort of bubbling hiss -- the kind you would expect, for example, from a rubber gasket that was allowing just a tiny bit of fluid+air seepage. You'd never hear it with the engine running. Encountering it was dumb luck.

I wasn't able to identify exactly where it was coming from -- the cap, one of the hoses clamped to it, or somewhere on the reservoir itself -- but I would say that (1) I have a leak and (2) the source is the reservoir itself or its joining to one thing or another.

So +1 to the "it's not supposed to just lose coolant", which I never really doubted, but wanted to come back and give you the solid confirm for my 2017 F56S. Pretty sure I won't like what I ultimately find out is leaking because for some reason I don't think it's the cap

 

With the car and engine and cooling system cold the cooling system was under low pressure. When you tapped the tank this jarred the cap and caused the cap to allow some air into the reservoir to balance the difference in pressure. Maybe.

Or the pressure could have been equalizing via a leak as you hypothesized. It is plausible.

As I touched upon in a previous post a hot pressure test is about the best way I know to find a coolant leak. I have seen leaks that didn't leak cold leak during a hot pressure test.

 

Thanx for continuing the discussion fellas, will be taking a more detailed/closer look around my system when I change my oil in the next week or so. I do know that my cap does hold some amount of pressure, as I 'popped' it open when the coolant was still a bit warm...forgetting that the expansion tank is under system pressure. Luckily no damage to me, wasn't full hot. Will give an update on what I find for coolant level as it has been a little while since I last topped off the system.

 

So I had a new issue come up, still can't figure it out...a 'strange' aroma coming from the rear of the engine compartment. Strange likely being some small critter starting to build a nest on my exhaust manifold/turbo?? Anywho, I did everything but pull my rear tube from the airbox to turbo to look down there, but couldn't find anything otherwise.

While I had the car up in the air and all kinds of various panels pulled off/out, it was time to change my oil/filter and put in a new air filter. While there, checked my coolant and it is still sitting nicely between MIN and MAX in the reservoir, so no loss in ~4 weeks now. While searching for the 'odor', I looked at every coolant hose connection I could find or track down and every one was bone dry and didn't show any evidence of residue as if an occasional leak. I am going to toss out that my particular coolant loss was just time/miles with some loss from the expansion tank cap venting. I may order up a new cap, but will keep tabs on things for the next couple of months before getting one on order.

I am almost wondering if my track day that I did with my Clubby back in 2018 had anything to do with it?? I did have ~2hrs out on track over 6 sessions where I wasn't particularly easy on the throttle. Who knows, but I certainly had fun that day and found some of the car's limits and handing traits.

 

So hey @RockC -- seems I have a confirmed coolant leak in my 2017 F56S. Still identifying source. Fun is in this thread over here -- would love your insights.

 

Well, figured I would give a 1 year update on my situation. I have been checking the coolant level every couple months and did not notice it move at all through my last check in mid-October 2023. I just checked it a couple of days ago and sure enough it is showing some loss (green line = full and red line = where it was at 12/27/23):




It turns out it took 8oz of coolant to bring it back up to between min/max on the level indicator in the reservoir (see below). Interesting to see that things stayed pretty level till we had the winter temp drop happen. This does lead me to believe that the loss is likely due to the reservoir cap venting some out each heat cycle as we transition from warmer to cooler temps here in the upper mid-west. If you take my findings from last season into account, there I had lost 64oz over 6 years or just over 10oz/year. This past year I saw ~8oz of loss, which is right on track with my previous loss, so nothing new and will obviously just keep the coolant level check every couple months on my list of things to review. Just to note, I still couldn't find any signs of a leak around/under the motor during my oil change earlier this year either.